The invention relates to polymer particles comprising a cross-linked polymer core and a linear non-cross-linked polymer shell. These polymer particles, which can be formed by emulsion polymerization, can be aggregated with colorant to form toner.
U.S. Pat. No. 6,767,684 to Patel et al., which is herein incorporated by reference in its entirety, describes an emulsion aggregation process for forming toner that combines both a latex containing a cross-linked resin and a latex containing a resin free of cross-linking. The process comprises, inter alia, mixing a colorant dispersion comprising an acicular magnetite dispersion and a colorant with the latexes, a wax dispersion, and a coagulant; heating the resulting mixture below about the glass transition temperature (Tg) of the latex resin to form toner sized aggregates; adding to the formed toner aggregates a further resin latex; adding a base to adjust the pH; and heating the resulting aggregate suspension to permit fusion or coalescence of the toner aggregates.